# Naos (Zeta Puppis)

Naos (Zeta Puppis) is a star in the constellation Puppis, magnitude 2.3.

**One of the hottest stars the eye can see — a runaway blue supergiant racing through the Milky Way.**

Few naked-eye stars are as extreme. Naos is a rare [O-type](https://astropilot.space/glossary/spectral-type) blue supergiant with a surface around 40,000 kelvin, so hot that most of its light pours out as ultraviolet we cannot see. Counting all of it, Naos shines hundreds of thousands of times as brightly as the Sun.

It is shedding itself fast. A wind blowing at 2,500 km per second carries off more than a millionth of its mass each year — about ten million times the Sun’s rate. It spins at over 220 km per second, close to breaking up, and it is a runaway, racing through space, perhaps flung out when a companion exploded as a supernova. It is heavy enough to end as one itself.

Its name is Greek for “ship”, fitting for the brightest star of Puppis, the stern of the ship Argo. In 1896 Williamina Fleming at Harvard found puzzling lines in its spectrum; they were later traced to helium that had lost an electron.

Naos (Zeta Puppis) is 1,100 light-years away: the light we see from it set off around AD 930, around the time al-Sufi described the Andromeda Galaxy in his Book of Fixed Stars.

## Did you know?

- **A patchy surface.** Naos dims by a mere 0.02 magnitude every 1.78 days. The cause seems to be bright patches at the base of its wind, carried round as the star turns.
- **One of eight.** Its mix of spectral features — evolved, yet spinning fast — is so unusual that only eight such stars are known in the Milky Way.
- **Another Suhail.** Arab astronomers called it Suhail Hadar, one of several bright southern stars that shared the name Suhail.

A blue-white 2nd-magnitude star, the brightest in Puppis, set in a rich Milky Way field south-east of Sirius and about seven degrees north of Gamma Velorum. Sweep the area with binoculars for its crowded starry background.

## When and where to see it

It is best placed in the evening sky around February, when it crosses the meridian at about 10 pm local time (around midnight in January). It can be seen from everywhere south of 50°N and never sets south of 50°S.

At its highest it stands below the horizon from 50°N, 15° up from 35°N, 50° up from the equator, 85° up from 35°S.

## Facts

- Type: Star
- Constellation: Puppis
- Designations: Zeta Puppis, ζ Pup, HR 3165, HD 66811, HIP 39429
- Magnitude: 2.3
- Position: RA 8h 3.6m, Dec −40° 0′ (J2000)
- Spectral type: O4I(n)fp
- Colour: blue-white (B−V -0.27)
- Distance: 1,100 light-years
- Discovered: Known since antiquity

Open AstroPilot to see when Naos (Zeta Puppis) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view. https://astropilot.space/object/naos